<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style type="text/css">
        .box {
            display: flex;
            flex-flow: row wrap;
            /**	justify-content: flex-start | flex-end | center | space-between | space-around;**/
            /** justify-content: flex-start;左对齐(默认)**/
            /**    justify-content: flex-end;右对齐**/
            /**  justify-content: center; 居中**/
            /**  justify-content:space-between;  两端对齐**/
            justify-content: space-around; /** 间隔 平分空闲区域**/

        }

        body {
            margin: 0;
            padding: 0;
        }

        div {
            padding: 25px;
        }

        .item1 {
            background: red;
        }

        .item2 {
            background: yellow;
        }

        .item3 {
            background: blue;
        }
    </style>
</head>
<body>
<div class="box">
    <div class="item1">1</div>
    <div class="item2">2</div>
    <div class="item3">3</div>
    <div class="item1">4</div>


</div>
</body>
</html>